What are those loud pops, booms and bangs in the Lake Minnetonka area?
Kara Schmitz was relaxing at home Thursday afternoon when a loud boom broke the silence and shook her Excelsior home.
"It didn't last long, maybe five seconds," Schmitz recalled, saying it sounded a lot like heavy object being dropped at a construction site.
Then it happened again on Saturday.
Others in Schmitz's neighborhood and in the small communities surrounding Lake Minnetonka have heard mysterious booming and popping sounds, too, and have taken to social media to ask what's behind the loud unsettling noises they have heard over recent days.
Chalk them up to a cryoseism — the technical term for an ice quake or frost quake — says Matt Benz, a meteorologist with Accuweather. Or at least that is the leading theory, he said.
Frost quakes happen most often when the ground is saturated and temperatures take nosedive. As precipitation in the ground freezes rapidly, it expands quickly and creates cracks in the soil. Loud pops occur when the ground cracks open, Benz said.
They are rare in Minnesota, but this relatively mild and snowless winter has brought all the ingredients for frost and ice quakes together, Benz said.
A much warmer December than usual saw nearly 2 inches of rain in the Twin Cities over Christmas Eve and Christmas Day. Without snow cover to insulate the ground, most of that moisture seeped into the ground. Then it rapidly froze when bitter arctic air arrived in mid-January, setting the stage for the below-ground action.
State Climatologist Luigi Romolo said he has not received any reports about similar noises in other parts of the metro, leading him to believe the creaking and groaning is likely coming from Lake Minnetonka. The ninth largest lake in the state didn't officially freeze over until Jan. 13, the latest ever for that to happen, according to the Climatology Office. At the same time, the first bout of subzero weather arrived, allowing ice to form at a much faster rate than normal.
The weight of the ice could cause fractures in the frozen liquid and produce ice quakes, Romolo said.
Schmitz, who lives directly across from Lake Minnetonka, said a neighbor saw a new crack in the ice 300 feet long and a foot wide along the shoreline after hearing a pop on Thursday.
But the sounds could also be resulting from cracks forming on land surrounding the lake, making them frost quakes, Romolo said.
"It is difficult to know," Romolo said. "We don't get them very often. We don't know very much about them."
What Romolo does know it that in most cases they don't pose much of a danger and they are "an environmental phenomenon that has little impact on our daily lives."
,Only in extreme cases do frost quakes cause damage to sidewalks, roads and foundations of buildings, Benz said.
Schmitz said the eerie sounds became the subject of a neighborhood chat group with curiosity leading most people to initially chime in.
But "it's starting to get a bit unnerving with the reports of how frequently it's happening in our area," she said. "Strange and exciting."
